1. Field of the Invention
The present invention relates to a dry etching apparatus. In particular, the present invention relates to an etching apparatus using plasma generated by applying a magnetic field or an electric field to a reaction gas introduced into a low-pressure chamber, and an etching method.
2. Description of the Related Art
Conventionally, there is a limit to a treatment ability of a dry etching apparatus, which causes problems in terms of enhancement of productivity.
In order to enhance a production efficiency, a mother glass size is increasing year after year. A currently used substrate has a size of 550 mm×650 mm, 650 mm×830 mm, etc. In the future, it is expected that a size of 850 mm×950 mm, a size of 950 mm×1000 mm, etc. will be used.
Conventionally, in-plane uniformity of etching tends to decrease with an increase in size of a substrate to be treated.
Japanese Patent Application Laid-open No. Hei 10-326772 discloses a technique of uniformly etching the entire surface of a substrate to be treated. Japanese Patent Application Laid-open No. Hei 10-326772 describes a parallel-plate type etching apparatus. In this apparatus, a lower electrode is separated into a ring shape, and the frequency of an AC electric field applied between the lower electrode and an upper electrode is varied. The separated lower electrode is connected to a low-frequency power source or a high-frequency power source.
The inventors of the present invention found that, when dry etching is conducted using a square or rectangular substrate, etching variations peculiar to the substrate are caused in a substrate surface.
Hereinafter, an etching method using a conventional parallel-plate type dry etching apparatus will be described.
Table 1 shows experimental results obtained by measuring variations in a substrate of etching using a parallel-plate type dry etching apparatus (electrode size: 50 cm×50 cm) by an RIE method.
TABLE 1Selection ratio of SiO2/a-Si at portions (A to I) in a substrate surfaceABCDEFGHISample3923.77825.515.310.471.811.47.41Sample30.413.919.882.722.379.973.410.72Sample5983.116.330.127.9667.87.81083Sample45.123.930.116.9106.910.57.411.811.44Etching conditions: CHF3=35 sccm, 800 W, 400 secAverage value of a selection ratio: 34.1, Minimum value of a selection ratio: 7, Maximum value of a selection ratio: 107.6
Table 1 shows selection ratios between a silicon oxide film and an amorphous silicon film at portions (A to I) shown in FIG. 21A. Four samples were arranged on the electrode as shown in FIG. 21B, and the etching was conducted. Etching was conducted using CHF3 as an etching gas with a flow rate of 35 sccm at 800 W (electric power density: 0.32 W/cm2) for 400 seconds, and the four samples were compared with respect to the portions.
As is understood from Table 1, the selection ratio at measurement point located in center portion of electrode is most uniform (30.4 to 59). On the other hand, the selection ratios of measurement points located in the comer portions of the electrode are very low as the measurement point exists away from the center portion of the electrode. That is, variations in the selection ratio of etching are caused in one substrate among four substrates shown in FIG. 21 B. For example, with respect to the substrate of sample 1, the selection ratio-of point I which is the most away from the center portion of the electrode is 7.4, the selection ratio of point G which is the nearest to the center portion of the electrode is 71.8. In the selection ratios of both points, about ten times difference is caused.
According to the experiment of the inventors of the present invention, the selection ratio of etching is largest at the center of a substrate, and decreases in a concentric manner as the measurement point exists away from the center portion of the electrode. In particular, the selection ratios at four comer portions (F to I) of the substrate are lowest. Thus, although the entire surface of a substrate should be etched with a uniform electric power density, variations in etching are caused. More specifically, in the case of using a rectangular substrate, a substantial electric power applied to the entire surface of a substrate becomes non-uniform, and an electric power density is varied between the central portion of the substrate and the comer portions thereof.
Therefore, in the case of using a conventional etching apparatus, the selection ratio at comer portions of an electrode becomes lowest, causing etching defects. The etching defects may decrease a yield. If a substrate is enlarged in the future, this problem is considered to become more conspicuous. The variations in etching are caused between the center portion of the substrate and the comer potion of the substrate when a big substrate with the same size as electrode is etched. The experiment results that four substrates are arranged on one electrode were shown here. Similar variations are also caused in case of a large substrate with the same size as electrode and in case of two substrates or more.
The problem involved in etching defects at corner portions of an electrode is not caused in the case where one circular substrate is used as in Japanese Patent Application Laid-open No. Hei 10-326772. That is, the problem that etching defects are caused in a rectangular substrate was found by the inventors of the present invention for the first time.